1. Field of the Invention
The present invention relates to a hinge device for coupling a member rotatably to another, and more particularly a hinge device for coupling two members, holding and inclining the first member to the second at any desired angle by virtue of friction.
2. Description of the Related Art
Lap-top personal computers and word processors comprise a main body and a rotatable unit such as a display unit, and a hinge device coupling the unit rotatably to the main body. Various hinge devices of this type are known, one of which has a bearing fastened to the main body, and a shaft rotatably supported by the bearing and connected at an end to the rotatable unit.
Some of the conventional hinge devices further have friction means designed to hold and incline the rotatable unit to the main body at a desired angle. The friction means includes a resilient member such as a wave spring or a belleville spring. The resilient member is interposed and compressed between the bearing and the flange formed on the shaft, thus exerting a friction force between the bearing and the flange. By virtue of this frictional force, the rotatable unit is held and inclined to the main body at any desired angle. If an external force greater than the frictional force is applied to the unit, the unit will be rotated in the direction the external force is applied.
The frictional force which the resilient member generates is applied in the axial direction of the shaft. The resilient member should have a greater spring constant than in the case where the frictional force is applied in the radial direction of the shaft. Further, the frictional force much depends on the size of the resilient member. If the resilient member has a size different from the design one, or has its size reduced due to wear, the frictional force will change greatly. To eliminate or reduce this change in the frictional force, a shim may be inserted between the resilient member and the flange or the bearing. The use of the shim is an addition of a component, and it is not easy to select the shim from many, which has the most appropriate thickness.
Since the resilient member exerts a force in the axial direction of the shaft, it needs to have a relatively large outside diameter in order to obtain an appropriate frictional drag. Consequently, the friction means is proportionally large, which makes it difficult to miniaturize the hinge device.